Using zammad behind nginx reverse proxy - Unable to login/sign up with Microsoft - nginx

Question

All zammad functionality is working fine except for login/signup with Microsoft
Error:
My nginx reverse proxy config is:
# Settings for a TLS enabled server.
upstream backend
{
server 192.168.99.99:443;
}
server
{
ssl on;
listen 9443 ssl http2 default_server;
ssl_certificate "/etc/pki/nginx/bundle.pem";
ssl_certificate_key "/etc/pki/nginx/private/tpsonline.com.key";
location /
{
proxy_set_header CLIENT_IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto https;
proxy_set_header X-Forwarded-Ssl on;
proxy_set_header Host $host;
proxy_pass https://backend;
}
}
}
My nginx config from zammad-helm is:
server_tokens off;
upstream zammad-railsserver {
server localhost:3000;
}
upstream zammad-websocket {
server localhost:6042;
}
server {
listen 8080;
server_name _;
root /opt/zammad/public;
access_log /dev/stdout;
error_log /dev/stderr;
client_max_body_size 50M;
location ~ ^/(assets/|robots.txt|humans.txt|favicon.ico) {
expires max;
}
location /ws {
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "Upgrade";
proxy_set_header CLIENT_IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_read_timeout 86400;
proxy_set_header X-Forwarded-Proto https;
proxy_set_header X-Forwarded-Ssl on;
proxy_pass http://zammad-websocket;
}
location / {
proxy_set_header Host $http_host;
proxy_set_header CLIENT_IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_read_timeout 180;
proxy_set_header X-Forwarded-Proto https;
proxy_set_header X-Forwarded-Ssl on;
proxy_pass http://zammad-railsserver;
gzip on;
gzip_types text/plain text/xml text/css image/svg+xml application/javascript application/x-javascript application/json application/xml;
gzip_proxied any;
}
}
What could be the reason that only functionality that's not working is sign up with microsoft?
p.s. i did follow these carefully: https://admin-docs.zammad.org/en/3.6/settings/security/third-party/microsoft.html
I did set headers as described in previous zammad issue https://github.com/zammad/zammad/issues/2758#issuecomment-536465142 but still no luck.